Announcing Rust 1.26.2
blog.rust-lang.org
blog.rust-lang.org
Participants range from "I'm interested in formal methods" to "my company uses formal methods and we're starting to apply them to Rust" to "The EU has given almost two million Euro for a university grant to prove Rust code" and everywhere in between :)
Steve - can you give me a source for the latter? I'd like to read more into that, specifically.
edit: this? https://joinup.ec.europa.eu/news/eu-funds-open-source-progra...
It's already borne some wonderful fruit. See https://www.ralfj.de/blog/2017/06/09/mutexguard-sync.html for an area where we were unsound, and https://github.com/rust-lang/rust/pull/45267#issuecomment-33... for an area where we were overly restrictive, and could remove some bounds without affecting soundness.
IMHO the current “Futures” monad style solution makes the code look a bit confusing.
The language currently knows nothing of coroutines. So, as you say, you chain Futures together, which is basically a monad. You submit that futures chain to an executor, like Tokio, and it basically moves the chain's stack to the heap, and then executes it. So, in some sense, Tokio is a stack-ful co-routine. It just so happens we know the stack's exact size at compile time, which has some nice properties compared to other stack-ful implementations.
Additionally, we have, in nightly, "generators." These are stack-less coroutines. On top of that, we have accepted (and there's a PR open in the compiler to implement) async/await. Async/await de-sugars to the whole Futures-chain shenanigans, but does it via generators. You then take that chain, and submit it to something like Tokio, making it stack-ful. Writing code with async/await is significantly more ergonomic than chaining futures together by hand, and feels more like goroutines, though suspension points are explicit rather than implicit.
Generators are likely to eventually be stable as well, so you can also write your own stack-less stuff if you want. But for now, they're an implementation detail of async/await, which has much less of a design surface area, and is what most people will want to do with this stuff, and so has priority.
Make sense?
I myself learned to program on node.js 6 years ago, when everything required piles of callbacks (the least ergonomic form of async/await style concurrency). It's strange to see a bunch of experienced programmers saying that nobody could possibly use this style, as it is too hard, while millions of beginning programmers master it easily. In fact I remember that the people who usually had a problem with callbacks were those who had prior experience with synchronous languages.
Async/await reveals the beauty of this pattern of async, by getting rid of the syntactical cruft of promises and callbacks. It's already awesome in C# and JS, and will be landing in Rust this year.
IMO using "thread" patterns should only be done when you actually have something to gain, with real multi core parallelism. The big advantage of coroutines is that they scale seamlessly across cores. By putting the bad ergonomics of threads everywhere, you make your code ready to scale onto actual threads.
One area in which async/await significantly improves over manual futures is borrows between individual futures in the chain. In languages with a GC, this isn't an issue, but it comes up in Rust a bunch.
See this for a great explanation: http://aturon.github.io/2018/04/24/async-borrowing/
Thanks for your work btw.
The problem with stackless concerns code reuseability. With stackless you have to duplicate all your intermediate functions: once for code that calls functions or methods which can yield, and again for code that takes functions or methods which won't yield. Or you simply don't reuse code at all, bifurcating the entire ecosystem.
The stackful vs stackless effectively refers to whether the implementation uses the same stack discipline for calls that can yield vs those that cannot. In either case you're always going to have to construct some kind of stack to support nested function invocation, the question is whether you're going to duplicate all that infrastructure.
Also, it helps if you don't conflate asynchronous I/O with coroutines. Coroutines are a meta abstraction over functions (an abstraction over call chains) that can be used to create ergonomic async I/O, but have other uses, like inverting producer/consumer caller/callee relationships (e.g. converting a push parser into a pull parser with a couple of lines of wrapper code). Stackful coroutines reuse the normal call stack discipline; stackless coroutines require function annotations and compiler rewriting and lead to the code reuse problems mentioned above.
Stackful coroutines are actually a perfect fit for Rust's ownership model, and would simplify much of the work, or obviate it altogether. But for other reasons--C compatibility, poor OS constructs for minimizing memory use, and an unfortunate early conflation of coroutines with async I/O--Rust has chosen the path of stackless coroutines a la async/await as the official model.
It's easy for beginners in the way GOTO spaghetti comes easy to beginners. That's all they know, after all. It however leads to bad designs and complex program flow.
let line = io::read_until(reader, b'\n', Vec::new());
let line = line.and_then(|(reader, vec)| {
if vec.len() == 0 {
Err(Error::new(ErrorKind::BrokenPipe, "broken pipe"))
} else {
Ok((reader, vec))
}
});
// Convert the bytes we read into a string, and then send that
// string to all other connected clients.
let line = line.map(|(reader, vec)| {
(reader, String::from_utf8(vec))
});
...
Maybe you prefer that, but I prefer the code to describe just the business logic.
let (reader, vec) = await { io.read_until(reader, b'\n', Vec::new() }?;
if vec.len() == 0 {
return Err(Error::new(ErrorKind::BrokenPipe, "broken pipe"));
}
let string = String::from_utf8(vec)?;I can only recommend trying it. It's magical!
Keyword arguments are something that we haven’t totally rejected, but many are skeptical. We’ll see!
Thanks for your answer!
Of course, I'm assuming you're imagining an implementation where you are allowed to omit keywords to set default values. Naturally if every argument is always required, you don't have this problem.